1008] on the Figure and Constitution of the Earth. 



99 



sphere with an inequality expressed by this harmonic would show in 

 one hemisphere a central elevation surrounded by a zone of depres- 

 sion, in the other a central depression surrounded by a ring of eleva- 

 tion. [Shown by slide.] This is something like what we observed 

 in the case of Australia in one hemisphere and the central Atlantic 

 in the other, but it is much too symmetrical. A more general type 



Fig. 1. 



of spherical harmonics of the third degree gives us an unsymmetrical 

 pear-shaped figure (Fig. 2) ; it is more like a natural pear than the 

 other. [Shown by slide.] The stalk is rather to one side, the waist 

 is higher on one side tlian the otlier, so is the protuberant ring, and 

 the crown is askew. When it is said, as it is sometimes, that the 

 figure of the earth is pear-shaped, it ought to be meant that the sur- 

 face has an inequality of this type. This figure is obtained by com- 

 bining the inequality which we examined just now with another 

 (Fig. ;3), which represents another special type of spherical harmonics 

 of the third degree. [Shown by slide.] Here we have, on one side, 

 elevation above and below and a central depression ; on the other 

 side, depression above and below, and a central elevation. A sphere 

 with an inequality expressed by this harmonic would show in either 

 hemisphere a circle surrounded by a ring ; half of the circle and the 

 alternate half of the ring are elevated, the other halves are depressed. 

 [Shown by slide.] Seen from a different point of view it would 

 show in one hemisphere a central band of elevation bordered by 



H 2 



